multiple alts, multiple lines, overwrite.

v0.2.7 (dev)

• restore multiple threads per annotation file after fix in biogo/hts (#64)
• add setid builtin to set the ID field and remove need for lua and fix some bugs.
• fix bug in self with multiple alternates when there were multiple overlaps (thanks Matthew).
• fix for #68, #69 -- with Number=A, op="self", the output will always have a number of elements
  equal to the number of alternates. If there are > 1 annos for a given site, later values will
  overwrite previous.